1990 1500 z71 w/5.7 TBI.I want to replace my evaporator core along with all other AC components. ALLdata tells me that this can be done from the passenger floorboard but everywhere else I look says the whole dash has to come out. Has anyone sucessfully done an evaporator replacement in this model truck? If so does the dash have to be removed or not? Thanks in advance!

I really don't see how they can make that claim - I'm not 100% sure to say it's impossible so I welcome anyone to offer evidence to support it, but I literally just do not see it. The box needs to be disassembled to get the evaporator core out.

The good news is that on 88-94 it's not a terrible job to get the dash out of the way so you can remove the box. Lower the steering column (don't forget to unclip the gear indicator wire from the column), remove the 5 screws across the top (1 under each speaker grille; pop the grilles up carefully), then 1 bolt under each side behind the kick panels - the dash can be tilted forward and will rest on the studs in the kick panel sheetmetal. Then you can disconnect wiring harnesses and lift the dash out of the truck. May have missed a step or two there but that's the overall picture.

The HVAC box has several screws through the engine side of the firewall. A couple are hidden including several behind the coolant reservoir bottle. Remove all the screws that look like that - the black 10mm head with the large captive washer.

Then on the inside, just to the driver side of the hump in the box that goes over the top of the evaporator core, there's a long 10mm head bolt that has to come out; you'll need a long extension. You can get an idea of its placement by looking on the engine compartment side and see the end of it poking out by the upper connection on the evap.

I've had several of these boxes out and it's no small job but again not a terrible one. It's the same basic process on 95-98 as well just those dashes are more work to remove.

Thank you for your response and the welcome! I have had several others tell me that the dash had to come out as well that is why it surprised me when I found this...

REMOVE OR DISCONNECT

Battery ground cable.
Coolant from the radiator.
Refrigerant from the system.
Coolant overflow tank.
Heater hoses from the coil tubes.
Refrigerant inlet (45) and discharge (46) lines from the evaporator.
Electrical connection to the temperature actuator.
Heater case bottom plate (50).
Remove the seven screws that hold the bottom cover.
Heater core.
Remove the screws and brackets that hold the core to the case.
Evaporator core cover (51).
Remove the four screws that hold the cover to the evaporator case.
Evaporator core.
Pull the core out and down from the evaporator case.
I hope to take a look at it this afternoon and see if this method makes any sense. If it does not I suppose out comes the dash lol. Thanks again man.

I guess I should have worded that differently. They didn't actually make the claim that the dash didn't have to be removed, however, they definitely didn't include it in the procedure. Maybe I was supposed to just assume that it had to come out first?

I did it from the passenger floor board. My box was cracked when I bought the truck so I needed to epoxy it back together. I cut the bottom the rest of the way off, switched the evaporator, and epoxied it back together.

Yes you can cheat like I did, but you should take the dash out. The bottom of mine was almost off to start with so that's why I did it that way. Cutting the rest of the box apart also made it easier to epoxy it back together so I could the epoxy between the joint. There is absolutely no way to get it from the floor without cutting.

Hey Jeff,
Thanks for the response. I took the 6 bolts out yesterday and removed the bottom cover of the HVAC box. There was one screw in the very back that was hard to get to but I finally got it out. I am going to pull the heater core this afternoon to see if I can gain further access to the evaporator core. Can you explain why you say the evaporator can't be removed without removing the dash?
I'm sure once I get the heater core out it will be obvious. I'm just looking for all the insight I can possibly get as I go through the process.

If you can separate the portion of the HVAC box that has the blower motor housing, you -might- be able to get the job done without pulling the dash. It looks like it could come down to whether you can access all the screws as well as wrangle the parts out.

Here's a view of the blower housing separated from the box, showing the evaporator core (covered in crud) - you can also see the 4 screw positions that hold the two pieces together.

Nope. Took all those out and still nothing. I believe you are correct in saying that the dash absolutely must come out. I have it half disassembled right now. The rest will come tommorow. It's time for . I do appreciate your help man.

Thank you for all the insight Richard. The job is now complete other than charging the system tommorow evening. I'm interested to see how this Sanden compressor performs compared the the R4 that I had. As for anyone who questions whether the dash has to come out in this model truck...absolutely lol

I will definitely let y'all know. Any advice on charging? It come with a charging chart stating between 70 to 80% of factory r12 charge. I have a 30lb cylinder and scales. Question is...when is enough? I'm used to charging by exact weight. This is going to be a little different.

Oh, one more thing. The paperwork that came with the compressor says that I need to rotate the compressor clutch manually by hand 10 times to clear all the oil from the compressor head. I'm a pretty big guy but I cannot move it by hand at all. Any ideas there? I had thought about bumping the a.c. button a time or 2 really quickly to accomplish this before I charge it. Would that work?

I always spin the compressor by hand to spread the oil so the compressor doesn't hydro lock. Like you, I had one that wouldn't. I locked the clutch figuring the belt would slip but it turned and worked fine ever since. Did you put all 8oz of oil in the compressor or did you put some in the accumulator and/or condenser?

Actually the compressor come precharged with 135cc or approximately 4.5 oz. The instructions with the kit says that this is a full charge of oil and specifically say not to add any oil to the system. I know originally the system takes 8 oz. Now I am confused.

Actually the compressor come precharged with 135cc or approximately 4.5 oz. The instructions with the kit says that this is a full charge of oil and specifically say not to add any oil to the system. I know originally the system takes 8 oz. Now I am confused.

Evidently the new style compressor doesn't need as much oil as the pancake compressor.

Man I am amazed myself. This is a world of difference. Prior to installing this kit I had the same temps that you did. The new kit had me relocated the orifice tube to the evaporator inlet. I can hear it pulsing now. Is that out of the ordinary?

No you don't. They will sell you whatever you want. They have a kit that is compressor upgrade only. The only reason that I replaced everything is because i have been fighting with trying to get this system to cool like it should for 2 years now with no luck. I figured if I threw a whole new system at it that it would work. I got lucky. Plus I figured it wouldn't hurt to swap out a 28 yr old evaporator lol.

great to hear.
Those are perfect temps. Dont want much colder than that.
you got lucky with the oil in the compressor.
Some come precharged. some have shipment oil that has to be swapped out and refilled. Some have none.
My 1990 had 55/2 but since I swapped cabs now I hav e55/3 because of the slifing back window lol

Old School GM fan FOREVER

Edited by rockfangd on 07-11-18 06:17 PM. Reason for edit: No reason given.

6. Turn bottle upside down so you get liquid only.
7. Open the HIGH PRESSURE valve.
8. Watch the gauges closely.
9. Immediately shut the high pressure valve when the system equalizes between high, and low pressure.
10. Turn the bottle back over.
11. Give it 5 minutes and start engine.

The system should be charged within a couple of ounces.

This does a couple of things. You are filling the liquid line, and pushing vapor across the orifice. As you watch the low pressure gauge you can tell if the orifice is operating correctly.

It also is filling the line that should be liquid during operation.

Yes, I know, "never charge liquid" (you'll lock the compressor up.

"Never open the high pressure side". You'll blow it up.

The system is down. Do NOT do this with the engine running!

This is a major time saver. Anyone that has ever tried to completely charge a new system using vapor only knows that you can grow old waiting.

Griff

Yes, I already know. There are going to be tons of naysayers shooting holes in my suggestion. As stated previously, I have worked on everything from Cats to Komatsus with Chevrolets, and Hyundais, even a couple of Fords.
I am IMACA certified, and I have done dozens of systems. This works.

So, that said, please don't state that it won't work unless you have tried it.

I'm not trying to be a jerk, but I don't need any theories, or opinions.

Love your response.
I deal with full size buses and They have alot of plumbing with their rooftop or skirt condensers.
Especially when the bus is 48 ft long. So there are hoses running to both the AC unit evaporator, and all the way to the condenser unit.
When I see a system that big that shows a proper charge of anything less than 5lbs or freon I call BS, and have proved it many times.
You talk about time. These new AC machines are absolutely ridiculous. They do all kinds of useless crap that you cannot control. Takes at least 1 hour to do a 15 minute job. Damn EPA